Waterborne polyurethane dispersions are well known in the coatings industry for their unique and strong performance properties including solvent and chemical resistance, mar and scuff resistance, excellent abrasion resistance, low temperature flexibility and good adhesion to a variety of substrates. However, for certain applications such as wood flooring, crosslinking of the polyurethane is needed to obtain the necessary performance requirements.
Current and future trends in performance coatings are centered on environmentally friendly or responsible polymer types that are based on more sustainable raw materials (by containing a high content of raw materials based on renewable resources) and can form coalesced films at low or reduced emissions of volatile organic compounds (reduced environmental impact). Waterborne polymers can offer improvements in reducing the level of volatile organic compounds released during film formation but they typically are based mainly on petroleum derived raw materials or lack the performance needed in certain applications such as wood flooring. This would be particularly true for one component self-crosslinking compositions which are more user friendly due to reduced toxicity concerns and more environmentally friendly due to less waste generated compared to more conventional two component crosslinked systems.
U.S. Pat. Nos. 4,066,591 and 4,147,679 disclose the preparation of waterborne polyurethane dispersions which contain unsaturated functional groups capable of undergoing auto-oxidative crosslinking.
U.S. Pat. No. 4,598,121 disclosed a method for preparing an, aqueous polyurethane dispersion, comprising (a) preparing a prepolymer with free NCO groups by reacting an aliphatic or cycloaliphatic polyisocyanate with a polyol, and an anionic compound; (b) dispersing said prepolymer in water; (c) reacting said water-dispersed prepolymer with a diamino hydrazide as a chain lengthening agent; and (d) reacting the prepolymer of step (e) in said dispersion with formaldehyde to effect crosslinking.
U.S. Pat. No. 4,983,662 disclosed an aqueous self crosslinkable coating composition comprising an aqueous dispersion of at least one polyurethane and having hydrazine (or hydrazone) functional groups and carbonyl functional groups disposed therein to provide a self crosslinking reaction, in which the polyurethane polymer takes part, via azomethine formation during and/or after film formation.
U.S. Pat. No. 5,070,136 disclosed an aqueous polymer dispersions essentially containing a copolymer of a) from 85 to 98.5% by weight of methacrylates, b) from 0.5 to 4% by weight of acrylic acid and/or methacrylic acid, c) from 0.5 to 4% by weight of acrylamide and/or methacrylamide, d) from 0.5 to 4% by weight of an α,β-ethylenically di-unsaturated or polyunsaturated compound and e) from 0 to 3% by weight of a carbonyl-containing α,β-ethylenically unsaturated compound, a process for their preparation, and their use for coating wood.
U.S. Pat. No. 5,141,983 disclosed a ketone-hydrazide crosslinking technology where the ketone, or carbonyl group resides on an acrylic polymer and a polyurethane polymer contains hydrazide functional groups. The composition is obtained by polymerizing the acrylic monomers in the presence of an aqueous polyurethane dispersion
U.S. Pat. Nos. 5,571,861 and 5,623,016 disclosed an aqueous, self-crosslinking polymer dispersion binder(s) comprising polyhydrazides and carbonyl-containing polyurethane-vinyl hybrid polymers and also, if desired, conventional additives are useful in base coatings, aqueous coatings, adhesives and printing inks.
U.S. Pat. No. 6,063,861 disclosed a storage stable, aqueous polyurethane-polyacrylate hybrid dispersions, which are self crosslinkable at room temperature and contain A) 10 to 95 wt. %, of a polyurethane dispersion, B) 5 to 90 wt. %, of a polymer prepared in the presence of component A) from a mixture of vinyl monomers containing 0.5 to 20 wt. %, based on the total resin solids content of the hybrid dispersion, of a vinyl monomer containing acetoacetoxy groups, and C) an at least difunctional primary or secondary amine, which is present in an equivalent ratio of amino groups to acetoacetoxy groups of 0.5:1 to 1.1:1, in which the wt. % of components A) and B) add up to 100, based on the total weight of components A) and B).
U.S. Pat. No. 6,239,209 disclosed waterborne urethane-acrylic compositions which are auto-oxidatively crosslinkable. In one embodiment, the composition also contains ketone hydrazide type self-crosslinking where the ketone/carbonyl is introduced via the acrylic and the hydrazide functionality is contained on the polyurethane along with the unsaturated oxidatively curable functional groups.
U.S. Pat. No. 6,576,702 disclosed waterborne polyurethane dispersions are prepared by reacting (1) at least one polyisocyanate; (2) at least one active hydrogen containing compound, such as a polyol or a polyamide; and (3) preferably also at least one water-dispersibility enhancing compound having water-dispersion enhancing groups, in order to form an isocyanate terminated prepolymer. The prepolymer subsequently is (1) optionally neutralized by reaction with at least one neutralizing agent, (2) dispersed in water, and then (3) chain extended by reaction with at least one of water, inorganic or organic polyamine having an average of about 2 or more primary and/or secondary amine groups, or combinations thereof. At least one plasticizer is introduced into the reaction mixture at any time during prepolymer formation or before the prepolymer is dispersed in water. The plasticizer substantially or completely replaces other organic diluents or solvents. Various types of plasticizers may be employed, including reactive plasticizers.